Field of the Invention
The present invention relates to a thermosetting (thermo-curable) resin composition for forming a self-lubricating liner of a sliding member such as an unlubricated sliding bearing and a reamer bolt, a sliding member provided with the self-lubricating liner, and a method for producing the sliding member.
Description of the Related Art
A sliding bearing in which a shaft of rotary motion or translational motion is held by a sliding surface has been widely used. In particular, an unlubricated sliding bearing using no lubricating oil for a sliding surface has been used for applications requiring low friction coefficient, high durability, high load capacity, high heat resistance, high oil resistance, and the like, such as vessel or ship application and aircraft application.
As such an unlubricated sliding bearing, Patent Literature 1 (Japanese Patent Application Laid-open No. 2007-255712 corresponding to United States Patent Application Publication No. 2007/223850) discloses a spherical bearing for high-load application including an outer race member having a concave first bearing surface and an inner race member having a convex second bearing surface slidably movable relative to the first bearing surface. In the spherical bearing, one of the outer race member and the inner race member is made of titanium alloy which has a bearing surface made of titanium nitride and formed on the titanium alloy surface by a physical vapor deposition method (PVD). The bearing surface of the other member includes a self-lubricating liner made from resin. The self-lubricating liner is composed of a fabric including fibers of polytetrafluoroethylene (PTFE) and polyaramid. The fabric is saturated with a phenol resin composition.
Patent Literature 2 (U.S. Pat. No. 6,180,574) discloses a self-lubricating coating composed of a thermosetting acrylic composition in which dipentaerythritol pentaacrylate is contained in an amount of 20% by weight or more and a solid lubricant such as polytetrafluoroethylene is contained in an amount of 10% by weight or more. Patent Literature 2 discloses that 20% by weight or more of triethylene glycol dimethacrylate and 1% by weight or less of aramid pulp may be added to the self-lubricating coating. Patent Literature 2 also discloses a sleeve bearing in which the self-lubricating coating is applied, as a liner, on the inner circumferential surface of an outer race.
Patent Literature 3 (Japanese Patent Application Laid-open No. 2011-247408 corresponding to United States Patent Application Publications No. 2011/262059 and No. 2014/169713) by the applicant of the present application discloses a sliding bearing suitable for the aircraft application and the like. The sliding bearing includes a self-lubricating liner formed on a sliding surface of the sliding bearing, and the self-lubricating liner is composed of a self-lubricating resin composition obtained by mixing 60% by weight to 80% by weight of polyether ketone resin, 10% by weight to 30% by weight of PTFE, 5% by weight to 15% by weight of carbon fiber, and 15% by weight or less of aramid fiber. The total content amount of the carbon fiber and the aramid fiber is 10% by weight to 25% by weight. A metal surface on which the self-lubricating liner is formed has a surface roughness Ra (average centerline roughness) of 4.0 μm or more and an Rmax (maximum height) of 30.0 μm or more.
Further, Patent Literature 4 (Japanese Patent Application Laid-open No. 2013-23554) discloses a thermosetting epoxy resin composition for a fiber-reinforced composite material capable of obtaining a cured product which not only has high heat resistance and high mechanical strength, but which is also excellent in impact resistance. The resin composition discloses in Patent Literature 4 includes: an alicyclic epoxy compound; a monoallyldiglycidyl isocyanurate compound; a curing agent; and a cure accelerator. Since a cured product obtained from the resin composition is excellent in heat resistance, mechanical strength and impact resistance, the cured product can be suitably used in structures such as fuselage, main wing, tail assembly, rotor blade, fairing, cowl and door of an aircraft; motor case and main wing of a spacecraft; body structure of an artificial satellite; automobile parts such as chassis of an automobile; body structure of railway carriage; body structure of a bicycle; body structure of a ship; blade for wind power generation; pressure vessel; fishing rod; tennis racket; golf shaft; robot arm; cable; and the like.
Since the unlubricated sliding bearings disclosed in Patent Literatures 1 to 3 are used by being incorporated into an aircraft and the like, the unlubricated sliding bearings are required to have low friction coefficient, high load capacity, heat resistance, oil resistance, and the like as described above. Further, from the side of airframe manufacturers, there is such a demand that in a step of assembling a sliding bearing such as a sleeve bearing, the manufactures wish to perform fitting adjustment through cutting or grinding of a sliding surface of the sliding bearing instead of performing a size adjustment on a shaft.
However, in the case of the fibrous lubricating liner described in Patent Literature 1, it is not possible to perform the size adjustment through the grinding or the cutting because, if it is subjected to such an after-processing, the fibers of the lubricating liner will be cut and the lubricating liner will not function as a liner any longer.
On the other hand, the self-lubricating coating based on thermosetting acrylic resin and described in Patent Literature 2 has wear resistance and friction coefficient under a high temperature which are not sufficient to be used by being incorporated into the aircraft and the like. There is a demand for a self-lubricating coating having higher wear resistance and lower friction coefficient under a high temperature. Further, when the size adjustment is performed through grinding or cutting the sliding surface of the sliding bearing, it is preferable that the thickness of the self-lubricating coating is thick so that the size adjustment can be performed in a wide range. However, in such a case that a thermosetting acrylic resin subjected to a relatively large thermal contraction (thermal shrinkage) during the thermo-curing process is used to form a thick self-lubricating coating, it is possible to occur a film separation, a film cracking, or the like.
Although the thermosetting epoxy resin composition disclosed in Patent Literature 4 has high heat resistance, this thermosetting epoxy resin composition is aimed to make the structures such as the fuselage, main wing and the like of an aircraft. Accordingly, it is not possible to apply the thermosetting epoxy resin composition as it is to a self-lubricating liner for the sliding bearing which is required to have various properties such as the sliding property, low friction coefficient, high load capacity, high oil resistance, and the like.
The self-lubricating liner described in Patent Literature 3 is based on the polyether ketone resin which is thermoplastic resin, and thus the self-lubricating liner can be produced by an injection molding method achieving high productivity. However, in order to improve the adhesion of the liner to the inner circumferential surface of the outer race, it is required that a shot blasting process for increasing the surface roughness of the inner circumferential surface of the outer race be performed beforehand. Further, in a case that PTFE is blended as a solid lubricant with the thermoplastic resin such as the polyether ketone resin, PTFE is required to be blended in an amount of less than 30% by weight, due to the following reason. During the kneading of resin and the injection molding, PTFE generates decomposition gas because it is heated to above its melting point by being exposed to high temperature and high pressure. From the viewpoint of safety, the generation of such decomposition gas should be prevented. Accordingly, the addition amount of PTFE should be limited. On the other hand, in order to improve the lubricating property of the liner, it is desirable that the addition amount of PTFE be increased.
Under the above circumstances, there is a demand for a resin composition for a self-lubricating liner which can ensure a sufficient addition amount of PTFE, can be handled easily during manufacturing steps, and requires no process for roughening the base surface.
The present teaching has been conceived to solve the foregoing problems. An object of the present teaching is to provide a resin composition for forming a self-lubricating liner which has low friction coefficient, high durability, high load capacity, high heat resistance and high oil resistance, as well as which can be subjected to a size adjustment through grinding or cutting after being cured, and which requires no process for roughening the base surface, and also to provide a resin composition which can be handled easily in manufacturing steps. Another object of the present teaching is to provide a sliding member with the self-lubricating liner composed of the resin composition.